You want the dragons, the war college, the rivalry that is obviously going somewhere, and a hero who keeps doing questionable things for the right reasons. That is a specific ask, and "romantasy" alone will not get you there.
Everything below is matched on what Fourth Wing actually is — enemies to lovers, high stakes, a magic school, a morally grey lead — rather than on the genre label, so the further down the list you go, the more one of those elements is swapped out for something else.
Rebecca Yarros · 623 pages · 2023
You asked for enemies to lovers and morally grey and dragons and magic school and high stakes — this has both.
Lauren Roberts · 500 pages · 2023
You asked for enemies to lovers and high stakes — this has both.
Holly Black · 370 pages · 2018
You asked for enemies to lovers and morally grey — this has both.
Leigh Bardugo · 465 pages · 2015
You asked for enemies to lovers and morally grey — this has both.
Leigh Bardugo · 358 pages · 2012
You asked for morally grey and magic school — this has both.
Samantha Shannon · 804 pages · 2019
You asked for dragons and high stakes — this has both.
Sarah J. Maas · 419 pages · 2015
You asked for morally grey — this has it.
Sarah J. Maas · 626 pages · 2016
You asked for morally grey — this has it.